Production of alcohols

ABSTRACT

BORIC ACID ESTER INTERMEDIATES IN THE PREPARATION OF ALCOHOLS OF NON-AROMATIC HYDROCARBONS ARE PRODUCED BY INTRODUCING BORIC ACID IN ADMIXTURES WITH WATER DIRECTLY INTO THE HYDROCARBONS UNDERGOING OXIDATION.

United States Patent "ice 3,651,153 PRODUCTION OF ALCOHOLS Gunther Strauss and Klaus Schneider, Mar], and Werner Jacquemin, Sythen, Germany, assignors to Chemische Werke Huls A.G., Marl, Germany No Drawing. Filed Aug. 24, 1965, Ser. No. 482,238 Claims priority, application Germany, Aug. 24, 1964, P 12 94 960.9-42 Int. Cl. C07c 35/02, 35/08, 31/02 U.S. Cl. 260-617 H 2 Claims ABSTRACT OF THE DISCLOSURE Boric acid ester intermediates in the preparation of alcohols of non-aromatic hydrocarbons are produced by introducing boric acid in admixtures with water directly into the hydrocarbons undergoing oxidation.

The-present invention relates generally to the production of alcohols by the oxidation of hydrocarbons in the presence of boric acid resulting in the formation of a boric acid ester of the hydrocarbon which is thereafter hydrolyzed to yield the desired alcohol.

It is known that aliphatic and cycloaliphatic hydrocarbons canbe oxidized in the liquid phase with oxygencontaining gases at elevated temperatures. The alcohols and monoketones formed in the foregoing reaction are further oxidized if allowed to remain in the oxidation zone to numerous undesired oxidation by-products, such as dihydric alcohols, diketones, carboxylic acids, and

resins.

It is furthermore known that the oxidation process can be controlled to proceed in the preferred direction toward the formation of alcohols, even at higher conversions, if the oxidation is conducted in the presence of an acid which is inert to the reactants. The acid is moreover esterified under the oxidation reaction conditions with the produced alcohols, thus protecting the formed alcohols from any further influence of the oxidizing agent. Particularly advantageous in this connection is the use of boric acid in such processes as exemplified in D-RPP (German Reich Patents) 552,886, 564,196, and U.S. Pat. No. 1,931,501. When the aforesaid oxidation process is conducted under such esterification conditions, it was necessary heretofore to use anhydrous boric acid, or boric acid anhydride. Such a mode of operation requires the utilization of special separation and dehydration processes in order to recover the dry boric acid, special devices for metering or dosing the solid boric acid, and other special devices for distributing and dispersing the boric acid in the hydrocarbon to be oxidized.

In order to avoid these disadvantages, the utilization of boric acid esters of low molecular weight alcohols has also described in connection with various processes. In these processes, it is additionally necessary to carry out the oxiation under substantially anhydrous conditions because of the notorious susceptibility of the boric acid esters to readily saponify in the presence of moisture.

Patented Mar. 21, 1972 Also, processes carried out in the foregoing manner require additional operations to produce the boric acid esters which are used in the process: DAS (German Published Application) 1,170,389 and French Pat. 1,166,679.

In yet another known process, an aqueous boric acid solution is admixed with the hydrocarbon feed. However, the water is thereafter removed from the mixture by azeotropic distillation, and the resulting anhydrous boric acidhydrocarbon suspension is the oxidized: Dutch Pat. 272,850 and published disclosure of Belgian Pat. 626,256. This process likewise requires the oxidation phase of the process to be conducted in the absence of water.

From French Pat. 1,351,666, it is known to add aqueous boric acid solution before or during the initiation of the process, loxydation initiale, i.e., during the so-called initial period, loc. cit., column 2, paragraph 3. According to this French patent, a specific distinction is made between the oxidation period proper and a preceding starting period or initiation period. During the oxidation proper, there is thus no water added; rather, the water has already been removed from the reaction mixture before the oxidation proper. This mode of operation thus corresponds to the process set forth in Dutch Pat. 272,850, i.e., the oxidation proper is conducted in the absence of water.

Summarizing, it is necessary and, in fact, essential according to the prior art described hereinbefore to conduct the so-called protective esterification of alcohols produced in the oxidation of hydrocarbons in the absence of water. The need for anhydrous reaction conditions can be more readily appreciated after a consideration of the fact that the boric acid esters are split in an ensuing hydrolysis step into the free alcohol and an aqueous boric acid solution solely by treating them with hot water. The fact that, in accordance with the present state of the art, the oxidation must be conducted in the absence of water is still further evidenced by reference to the following: Chimie et Industrie (Chemistry and Industry), vol. 91, pp. 519- 528 (1964); Petrochemie (Petrochemistry) USSR I, 2, pp. 224254 (1961); Petrochemie (Petrochemistry) USSR I, 4, pp. 527-539 (1961); O1- und Fettindustrie (Oil and Fat Industry) USSR 4, pp. 2629 (1963); Chem. Wiss. Ind. (Chemical Science and Industry) USSR 1, p. 273 (1956).

In a broad aspect, it is an object of this invention to provide an improved process for the production of alcohols from the hydrolysis of boric acid esters thereof which esters have been obtained by oxidizing hydrocarbons in the presence of boric acid.

It is a further object of this invention to provide in the present process for the production of alcohols an improved method of recovering and recycling to the oxidation step the boric acid obtained by hydrolyzing the ester thereof.

It is yet another object of this invention to provide a continuous series of oxidation saponification reactions wherein the exothermic heat of reaction is rapidly and efficiently removed by the reaction medium as heat of vaporization thereof.

Upon further study of the specification and appended claims, other objects and advantages of the present invention will become apparent.

It has been surprisingly discovered that alcohols can be advantageously produced and the above objects accomplished, by oxidizing aliphatic or cycloaliphatic (i.e., non-aromatic) hydrocarbons in the liquid phase with oxygen-containing gas at elevated temperatures and conditions favoring the formation of boric acid esters, and thereafter hydrolyzing the produced esters to yield the desired alcohols, if, over the span of the entire oxidation period, aqueous'boric acid is continuously admixed with the hydrocarbon feed in an amount corresponding to the amount of alcohol produced.

Hydrocarbons found particularly suitable for use in the present oxidation process are saturated aliphatic hydrocarbons containing at least 10 carbon atoms and cycloaliphatic hydrocarbons containing at least 6 carbon atoms and mixtures thereof. That is to say, any nonaromatic hydrocarbon being in liquid phase under reaction conditions can be oxidized.

Examples of suitable cycloaliphatic hydrocarbons include cyclohexane, cycloheptane, cyclooctane, cyclononane, particularly cyclodecane, cycloundecane, and cyclododecane. Also polycyclic cycloaliphatic hydrocarbons e.g. perhydronaphthalene and unsaturated cycloaliphatic hydrocarbons e.g. tetrahydronaphthalene can be used.

Aliphatic hydrocarbons can be, for example, decane, undecane, dodecane, tridecane, tetradecane. In addition. there can also be employed branched chain isomers of the precedingly described saturated aliphatic hydrocarbons,

as well as their correspondingly unsaturated compounds.

Mixtures of the foregoing compounds can be used which, for example, are produced when certain narrow boiling cuts of the above-mentioned paraffius are obtained from the fractionation of hydrocarbons.

Among the various forms of aqueous boric acid found suitable herein, it is desirable to use moist, crystalline orthoboric acid which is precipitated, for example, from the hot aqueous boric acid solution obtained from the hydrolysis of the boric acid esters produced during the oxidation. This particular boric acid can be obtained from hot aqueous boric acid solution (generally 90 C.) by filtration or centrifugation, after cooling the boric acid solution to room temperature, preferably cooling by vacuum evaporation. Another form of aqueous boric acid suitable is an aqueous solution of ortho boric acid saturated at 90 C. (containing about 30% by weight ortho boric acid). Such moist boric acids generally have a water content of about to 30% by weight.

It is particularly advantageous to use as a source of boric acid the hot-saturated aqueous boric acid solution itself, as produced from the saponification of the boric acid esters. This hot boric acid solution having generally a temperature of about 90100 C., can be removed from the hydrolysis step in this form without difficulty and recycled to the oxidation stage; hence, the boric acid contained therein is subjected to a constant recycling process.

It is especially advantageous to use only a minimal quantity of water to hydrolyze the boric acid esters formed in the oxidation reaction; preferably, the hydrolysis is carried out in a counter-current washer in a manner such that the boric acid esters are quantitatively saponified, and the quantity of water present is just sufiicient to form a boric acid solution saturated at a temperature of about 90l00 C. Still another way of reducing the amount of water used in the cycle is to conduct the saponification of the boric acid esters under elevated pressures which permits the use of the higher solution temperatures which in turn provides for a high dissolution and a concomitant high concentration of the boric acid therein. In such a mode of operation temperatures and pressures are employed, for example pressures from 1 to 2 atmospheres and temperatures of 100 to 120 C. which will not require any type of special equipment.

The hydrolysis is conducted by adding to the boric acid ester only enough water to saponify the ester and form 4 a resulting boric acid solution saturated at a temperature of about -120 C.

The amount of boric acid charged to the reactor is dependent, as stated hereinbefore, upon the conversion of the hydrocarbon to the boric acid ester thereof. That is to say, it is added in equivalent amounts corresponding to the equivalents of the produced alcohol. Preferably the reaction solution contains an excess of 1 to 20, especially 2 to 10% of boric acid, with reference to the boric acid present in the boric acid ester. The preferred mode to control the feed of boric acid is accomplished by continuously analyzing the produced alcohol in the reactor and controlling the flow of the aqueous boric acid by an automatically controlled valve disposed in the boric acid feed line to the reactor. The water introduced by the aqueous boric acid vaporizes immediately so that it is completely eliminated in the reaction zone, that is to say it is not present in a concentration sufficient to reverse the esteri-fication reaction by hydrolysis. (The amount of water is so small, that it is not troublesome to the esterification reaction.)

The oxidation of the hydrocarbons is conducted under conventional conditions, for example, temperatures be tween and 190 C., preferably between 1 60 and C. If required, superatmospheric pressures, ranging for example, from 1 to 3 atmospheres gage may be utilized, but preferably atmospheric pressure is used. When the oxidation process is carried out in the aforesaid manner a conversion of the hydrocarbon ranging between 5 to 40% is obtained.

Preferred molecular oxygen-containing gases for use in this invention are those having 3 to 21 volume percent of oxygen. Advantageously, air can be employed, diluted if desired by inert gases such as nitrogen. The oxidation process can be conducted in a discontinuous as well as continuous manner; however, the continuous mode of operation is preferred. However, if the oxidation process is to be conducted discontinuously, the temperature of the aqueous boric acid hot solution or moist crystalline boric acid charged to the hydrocarbon is preferably adjusted to the reaction temperature when or before the oxygen containing gas is first admitted.

The process of this invention can also be carried out continuously at a rate dependent on rate of the alcohol formation, i.e. the aqueous boric acid is fed maximally in equivalent amounts with respect to the alcohol obtained in the oxidation process. The aqueous boric acid is advantageously sprayed into the reactor through a spray nozzle which is positioned in the reactor so as to discharge a short distance below the level of the liquid therein. The vaporizing water together with the rising oxidation waste gases are removed from the reactor, and hydrocarbon feed which is entrained in these rising gases is separated therefrom and recycled back to the reactor. A particularly advantageous feature manifest in the continuous mode of operation employing a constant aqueous boric acid feed rate is that the exothermic heat of reaction liberated by the oxidation process can be removed predominantly and simply by vaporizing the charged water without resort to additional apparatus.

In addition to the foregoing pyrometric advantages and the improved energy balance resulting therefrom, a disadvantage of the known processes is obviated by eliminating the step of dehydrating the aqueous solution pro- .duced during the saponification of the boric acid esters in order to obtain dry, anhydrous boric acid. Further to this, no special equipment is required to carry out the latter purification and no additional energy is required since the Water is not evaporated before the oxidation reaction proper. Furthermore, the inherent difiiculties arising when a fine-particulate powder is dispensed into the reactor are obviated i.e. entrainment of such powder in the waste gas leaving the reactor, and the danger of clogging the feeding devices necessary for the proportionate charging operation.

In the event the entire oxidation process is conducted continuously, the hydrocarbon is fed to the oxidation reactor at a rate corresponding to the conversion of the hydrocarbon and the desired residence time in the reactor. The reaction product is also removed from the reactor in the same manner, viz., the rate of removal corresponds to the conversion rate and the oxidation process can be advantageously divided into a conventional series of individual stages, for example by using a cascade system. However, the feeding of the boric acid, particularly when it takes the form of an aqueous boric acid solution as recovered from the hydrolysis stage, is conducted in precisely the same continuous manner as described hereinbefore for the discontinuous oxidation. When the oxidation is split into several individual stages, it is of course possible to distribute the boric acid solution selectively among the various individual stages, in correspondence with the respective conversion in the individual stages.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the specification and claims in any way whatsoever.

EXAMPLE 1 Comparative example (a) To an agitated vessel having a 20 m. capacity, 12,000 kg. of eyclododecane feed are charged, at 150 to 180 C., over a span of about 4 to 5 hours. There are also charged to the reactor 400 m. /hr. of air of which about 80% of the oxygen therein is consumed during the oxidation reaction. In addition, 100 kg./hr. of boric acid anhydride are continuously added to the oxidation mixture during the course of the reaction. After a conversion of 33%, the oxidation reaction is interrupted and the resulting boric acid ester is thereafter saponified at 90 C. with 2200 liters of water to yield a saturated boric acid solution in admixture with the products of oxidation. After separating the boric acid solution from the product, the latter product is then purified in a conventional manner by fractional distillation thereof. The yield of cyclododecanol/-one is 80.5% of theoretical based on the reacted hydrocarbon.

(b) Under the conditions set forth above in Example 1(a), 170 kg./hr. of moist orthoboric acid crystals are fed, in accordance with the invention, continuously into the eyclododecane which is to be oxidized a-short distance below the level of the liquid. The moist orthoboric acid was produced by centrifuging the crystals obtained by cooling a hot hydrolysis boric acid solution. Water vapor together with residual air is removed and separated from the eyclododecane entrained therein and the latter is then recycled to the reactor. After saponifying the boric acid esters, the yield, at a 33% conversion, is 81.6% of the theoretical cyclododecanol/-one.

EXAMPLE 2 Under the conditions disclosed in Example 1(a), boric acid, in the form of an aqueous boric acid solution saturated at 90 C., is sprayed continuously into the reaction mixture a short distance below the level of the liquid, the hourly quantity being 440 liters. The water is removed, as in Example 1(b) together with the residual air and separated from entrained eyclododecane, the latter being recycled into the reactor. At a conversion of 33 the yield in cyclododecanol/-one (5:1) amounts of 79.8% of theory.

EXAMPLE 3 In this example, 500 kg. eyclododecane are added to a stirrer vessel of 1 m. capacity to illustrate a continuous air oxidation process. At a temperature of about 170 C.,

25 mfi/hr. of air are supplied from which about of the oxygen is consumed. The fresh eyclododecane is fed into the reactor at a rate of kg./hr. and a corresponding quantity of the resulting oxidized product is continuously withdrawn and passed on to further processing. Through a spray nozzle tube inserted at a short distance below the level of the liquid reactants, about 40 l./hr. of an aqueous solution of orthoboric acid (equivalent to an acid addition rate on a dry basis of approximately 8.4 kg./ hr.) maintained at a temperature of about 95 C. are continuously fed to the oxidation reaction mixture.

When employing a residence time in the reactor of 4 hours, about a 25% conversion of eyclododecane is obtained and a combined yield of cyclododecanol and cyclododecane based thereon of 78 mole percent is obtained from the subsequent product purification process. The two foregoing oxidized hydrocarbons are produced in a ratio of 4:1, respectively.

EXAMPLE 4 In a stirrer vessel of 20 m5 capacity, 9,000 kg. of n-tetradecane are oxidized. After heating the n-tetradecane to 190 C., 400 m. /hr. of air are continuously blown therethrough over a span of 4 hours, the oxygen consumption amounting to about 80%. During the entire reaction period, 398 kg./hr. of a 20% solution of orthoboric acid maintained at a temperature of 90 C. are fed into the reactor through a spray nozzle tube which exits a short distance below the level of the liquid. Under slight forming conditions the water content of the boric acid solution is rapidly vaporized and separated from the entrained reactants in a waste gas cooler. Entrained liquid n-tetradecane is thereby reversed and flows back into the reactor.

After the oxidation reaction is terminated, the desired product is thereafter liberated from the ester in a conventional manner by means of hydrolysis, and the yield is determined.

At a conversion of 22% of the n-tetradecane originally charged, there results an n-tetradecanol/-one yield of 71% of the theoretical. The ratio of produced alcohol to ketone is about 4: 1, respectively.

The preceding examples can be repeated with similar success by substituting the generically and specifically described reactants and operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and condit1ons.

What is claimed is:

1. A continuous process for the production of alcohol from a non-aromatic hydrocarbon selected from the group consisting of aliphatic hydrocarbons containing at least 10 carbon atoms, cycloaliphatic hydrocarbons containing at least 6 carbon atoms and mixtures thereof, said process comprising:

(a) oxidizing said hydrocarbon in the liquid phase at about 190 C. in the presence of boric acid to produce a boric acid ester;

(b) hydrolyzing said ester with only enough water to produce said alcohol and an aqueous boric acid solution saturated at a temperature of about 90-120" 0.;

(c) continuously passing said boric acid solution to said liquid phase hydrocarbon in step (a) at a rate corresponding to the formation rate of the boric acid ester and wherein the water added with the boric acid is vaporized by the exothermic heat liberated by the oxidation of the hydrocarbon and the resulting water vapor is continuously removed from the reaction medium.

7 2. The process of claim 1 wherein said hydrolyzing is a FOREIGN PATENTS conducted at a pressure of from about 1-2 atmospheres 914 510 Great Britain 3 gauge and said aqueous boric acid solution is saturated at 1 351666 12/1963 France B a temperature of about IOU-120 C.

5 OTHER REFERENCES References Cited Bushkivov et' 611.: World Petr. Congress, 5th pro- UNITED STATES PATENTS ceedings, New York, v01. 4, pp. 175 to 187 (1960).

1,947,989 2/ 1934 Hellthaler et a1. 260631 B 2,721,180 10/1955 Lawrence et a1. 260-631 B BERNARD HELEN Pmnay Exammer 3,317,581 5/1967 Becker 260631 B 10 J. E. EVANS, Assistant Examiner 3,346,614 10/1967 Starks et a1. 260462 OX 3,420,897 1/1969 Russell et a1 260631 B 3,442,959 5/ 1969 Suierman 260462 0X 23-199; 260586 B, 593' R, 617 F, 631 B, 639 B 3,445,512 5/1969 Webster et a1. 260537 

